Fluid cooler bypass valves are used in conjunction with engines, transmissions, power steering systems, hydraulic systems and other systems that heat a working or lubricating fluid. They are designed to provide a flow path by which fluid delivered to the valve from the heat source is returned without passing through a fluid cooler such as a radiator or other heat exchanger during warm-up periods.
Typical fluid cooler bypass valves include an actuator which responds to temperatures above a set-point to move a valve member from a bypass position where fluid is permitted to flow from the source of heated fluid to the fluid cooler return path without passing through the fluid cooler. Prior art bypass valves move from a bypass position where a bypass passage is open and the flow path to or from a cooler is obstructed to a steady state (cooling) position where the bypass passage is closed and the flow path to and from the fluid cooler is open. The fluid flow path can be re-configured using a single valve member.
The use of wax-filled actuators, otherwise referred to as wax motors, as thermally responsive control devices in fluid circulation systems is well known. Wax motors have been used as temperature sensitive actuators for valves employed in fluid cooling systems to control flow paths for fluid during warm-up and steady state operating conditions. Such bypass valves are designed to open or close in response to a predetermined change in temperature. Wax motors require no external power source, are reliable, extremely compact and powerful for their size.
Wax motors typically include a housing having a chamber filled with thermally responsive wax contained beneath a flexible diaphragm. The wax expands as temperature increases, exerting an outward force on the diaphragm and on a reciprocating piston disposed on the other side of the diaphragm. Movement of the piston is controlled by a guide extending from the actuator housing. The wax motor is constructed such that known changes in temperature produce predetermined axial movement of the piston with respect to the housing.
Consequently, there exists a need for a thermally actuated flow control valve with pressure relief capability that employs a simplified mechanism to provide warm-up and steady state flow paths in a fluid cooling system.